Pile driving and pile pulling equipment, hereinafter collectively referred to as pile driving equipment, is used to drive large piles into the earth to form a stable support for buildings or other structures. Similarly, the pile driving equipment is used to remove large piles from the earth. U.S. Pat. No. 5,117,925 discloses pile driving equipment with a vibratory apparatus that imparts a vibration force to the pile. These vibratory pile driving devices have recognized several advantages over pile driving equipment that uses hammer devices to drive the pile, including an increased driving speed.
The vibratory apparatus to generate extremely high driving and pulling forces by rapidly rotating large counterweights within vibratory assembly. The counterweights are large cylindrical, eccentrically weighted gears, i.e., they have an uneven weight distribution around the body of the gear such that its center of gravity is radially outward of the gear's rotational axis. When the vibratory apparatus rapidly rotates two counterweights in opposite directions, the counterweights generate substantial vibratory forces that are transmitted through the vibratory assembly, through a pile holding device, and to the pile. However, this rapid rotation also creates large stress loads within the counterweights themselves. High temperatures in and around the counterweights are also generated, because friction between the moving components.
The prior art includes a vibratory assembly with counterweights having a solid eccentric weight bolted to a portion of a cylindrical gear. These bolted counterweights are not sufficiently durable, because the bolts have a very undesirable tendency to break under the large stress loads generated during rotation counterweights. Another prior art vibratory assembly avoids this breaking problem by using a cast, one-piece, solid counterweight having an eccentric weight portion integral with a cylindrical gear portion. These solid, cast counterweights, however, do not have sufficient mass to generate large enough vibratory forces to efficiently drive or pull piles.
Attempts have been made to increase the mass of such cast counterweight by machining or casting bores in the eccentric weight portion, pouring molten lead into the bores, and allowing the lead to cool and solidify. These lead-filled counterweights, however, produce a limited degree of vibration amplitude in that one rotation of such counterweights only moves the vibratory apparatus vertically less than one inch. In addition, the elevated temperatures from the friction between moving components cause the lead to become somewhat fluid and shift during operation. The shifting lead results in unbalanced weight distribution in the counterweights, which creates undesirable lateral forces that can damage the vibratory assembly. Although the prior art devices lubricate the moving components with oil, the amount of friction is still sufficient to generate high temperatures. The balance problem is also partially caused by the inability to fill the bores with precise amounts of molten lead.
Yet a further problem experienced with lead-filled counterweights is that the lead inserts can be chipped or shaved off during operation, or otherwise contact the oil, and the loose lead contaminates the oil and creates an environmentally hazardous waste. This hazardous waste requires proper and expensive disposal procedures.
As a result of the above-described limitations, there have not heretofore been acceptable solutions to the problems of providing a vibratory assembly that is durable, easy to manufacture, sufficiently balanced, and capable of withstanding elevated temperatures without producing disadvantageous lateral forces and environmentally hazardous waste material and lower vibratory force than desired.